New Findings r What is the central question of this study?Does the combination of a higher neural respiratory drive and greater dynamic mechanical ventilatory constraints during exercise in healthy women versus men form the mechanistic basis of sex differences in activity-related dyspnoea? r What is the main finding and its importance?Sex differences in activity-related dyspnoea in health primarily reflected the awareness of a higher neural respiratory drive needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical ventilatory constraints in women. These findings may have implications for our understanding of the mechanisms of sex differences in exertional dyspnoea in variants of health (e.g. the elderly) and in patients with cardiorespiratory disease.The purpose of this study was to elucidate the physiological mechanisms of sex differences in exertional dyspnoea. We compared detailed measures of neural respiratory motor drive [diaphragmatic EMG (EMGdi) expressed as a percentage of maximal EMGdi (EMGdi%max)], breathing pattern, operating lung volumes, dynamic respiratory mechanics [tidal oesophageal (P oes,tidal %peak) and transdiaphragmatic pressure swings (P di,tidal %peak) expressed as a percentage of their respective peak values] and sensory intensity and unpleasantness ratings of dyspnoea during symptom-limited incremental cycle exercise in healthy young women (n = 25) and men (n = 25). The tidal volume to forced vital capacity ratio (V T %FVC), breathing frequency, EMGdi%max, P oes,tidal %peak, P di,tidal %peak and sensory intensity and unpleasantness ratings of dyspnoea were higher, while dynamic inspiratory capacity and inspiratory reserve volume were lower at a standardized absolute ventilation of 55 l min −1 during submaximal exercise in women versus men (all P < 0.05). In contrast, sex had no demonstrable effect on the inter-relationships between exercise-induced increases in V T %FVC, EMGdi%max and sensory intensity and unpleasantness ratings of dyspnoea. The results of this study suggest that sex differences in the intensity and unpleasantness of exertional dyspnoea in health are likely to reflect the awareness of a relatively higher neural respiratory motor drive (or EMGdi%max) needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical constraints on V T expansion in women.

We tested the hypothesis that neuromechanical uncoupling of the respiratory system forms the mechanistic basis of dyspnea during exercise in the setting of "abnormal" restrictive constraints on ventilation (VE). To this end, we examined the effect of chest wall strapping (CWS) sufficient to mimic a "mild" restrictive lung deficit on the interrelationships between VE, breathing pattern, dynamic operating lung volumes, esophageal electrode-balloon catheter-derived measures of the diaphragm electromyogram (EMGdi) and the transdiaphragmatic pressure time product (PTPdi), and sensory intensity and unpleasantness ratings of dyspnea during exercise. Twenty healthy men aged 25.7 ± 1.1 years (means ± SE) completed symptom-limited incremental cycle exercise tests under two randomized conditions: unrestricted control and CWS to reduce vital capacity (VC) by 21.6 ± 0.5%. Compared with control, exercise with CWS was associated with 1) an exaggerated EMGdi and PTPdi response; 2) no change in the relationship between EMGdi and each of tidal volume (expressed as a percentage of VC), inspiratory reserve volume, and PTPdi, thus indicating relative preservation of neuromechanical coupling; 3) increased sensory intensity and unpleasantness ratings of dyspnea; and 4) no change in the relationship between increasing EMGdi and each of the intensity and unpleasantness of dyspnea. In conclusion, the increased intensity and unpleasantness of dyspnea during exercise with CWS could not be readily explained by increased neuromechanical uncoupling but likely reflected the awareness of increased neural respiratory drive (EMGdi) needed to achieve any given VE during exercise in the setting of "abnormal" restrictive constraints on tidal volume expansion.

In a randomized cross-over study of 15 healthy men aged 20–30 years, we compared physiological and perceptual responses during treadmill and cycle exercise test protocols matched for increments in work rate — the source of increased locomotor muscle metabolic and contractile demands. The rates of O2 consumption and CO2 production were higher at the peak of treadmill versus cycle testing (p ≤ 0.05). Nevertheless, work rate, minute ventilation, tidal volume (VT), breathing frequency (fR), inspiratory capacity (IC), inspiratory reserve volume (IRV), tidal esophageal (Pes,tidal) and transdiaphragmatic pressure swings (Pdi,tidal), peak expiratory gastric pressures (Pga,peak), the root mean square of the diaphragm electromyogram (EMGdi,rms) expressed as a percentage of maximum EMGdi,rms (EMGdi,rms%max), and dyspnea ratings were similar at the peak of treadmill versus cycle testing (p > 0.05). Ratings of leg discomfort were higher at the peak of cycle versus treadmill exercise (p ≤ 0.05), even though peak O2 consumption was lower during cycling. Oxygen consumption, CO2 production, minute ventilation, fR, Pes,tidal, Pdi,tidal and Pga,peak were higher (p ≤ 0.05), while VT, IC, IRV, EMGdi,rms%max, and ratings of dyspnea and leg discomfort were similar (p > 0.05) at all or most submaximal work rates during treadmill versus cycle exercise. Our findings highlight important differences (and similarities) in physiological and perceptual responses at maximal and submaximal work rates during incremental treadmill and cycle exercise testing protocols. The lack of effect of exercise test modality on peak work rate advocates for the use of this readily available parameter to optimize training intensity determination, regardless of exercise training mode.

We tested the hypothesis that elastic binding of the abdomen (AB) would enhance neuromuscular efficiency of the human diaphragm during exercise. Twelve healthy non-obese men aged 24.8 ± 1.7 years (mean ± SE) completed a symptom-limited constant-load cycle endurance exercise test at 85% of their peak incremental power output with diaphragmatic electromyography (EMGdi) and respiratory pressure measurements under two randomly assigned conditions: unbound control (CTRL) and AB sufficient to increase end-expiratory gastric pressure (Pga,ee) by 5-8 cmH 2 O at rest. By design, AB increased Pga,ee by 6.6 ± 0.6 cmH 2 O at rest. Compared to CTRL, AB significantly increased the transdiaphragmatic pressure swing-to-EMGdi ratio by 85-95% during exercise, reflecting enhanced neuromuscular efficiency of the diaphragm. By contrast, AB had no effect on spirometric parameters at rest, exercise endurance time or an effect on cardiac, metabolic, ventilatory, breathing pattern, dynamic operating lung volume, and perceptual responses during exercise. In conclusion, AB was associated with isolated and acute improvements in neuromuscular efficiency of the diaphragm during exercise in healthy men. The implications of our results are that AB may be an effective means of enhancing neuromuscular efficiency of the diaphragm in clinical populations with diaphragmatic weakness/dysfunction.

BackgroundWith over 230 million surgical procedures performed annually worldwide, better application of evidence in anesthesia and perioperative medicine may reduce widespread variation in clinical practice and improve patient care. However, a comprehensive summary of the complete available evidence has yet to be conducted. This scoping review aims to map the existing literature investigating perioperative anesthesia interventions and their potential impact on patient mortality, to inform future knowledge translation and ultimately improve perioperative clinical practice.MethodsSearches were conducted in MEDLINE, EMBASE, CINAHL, and the Cochrane Library databases from inception to March 2015. Study inclusion criteria were adult patients, surgical procedures requiring anesthesia, perioperative intervention conducted/organized by a professional with training in anesthesia, randomized controlled trials (RCTs), and patient mortality as an outcome. Studies were screened for inclusion, and data was extracted in duplicate by pairs of independent reviewers. Data were extracted, tabulated, and reported thematically.ResultsAmong the 10,505 publications identified, 369 RCTs (n = 147,326 patients) met the eligibility criteria. While 15 intervention themes were identified, only 7 themes (39 studies) had a significant impact on mortality: pharmacotherapy (n = 23), nutritional (n = 3), transfusion (n = 4), ventilation (n = 5), glucose control (n = 1), medical device (n = 2), and dialysis (n = 1).ConclusionsBy mapping intervention themes, this scoping review has identified areas requiring further systematic investigation given their potential value for reducing patient mortality as well as areas where continued investment may not be cost-effective given limited evidence for improving survival. This is a key starting point for future knowledge translation to optimize anesthesia practice.Electronic supplementary materialThe online version of this article (10.1186/s13643-018-0863-x) contains supplementary material, which is available to authorized users.